Delete Rows In Txt Input File BEFORE Searching For Data

I read in a txt file with the code below. There's some kind of special character in the last 3 lines of the input file that makes the macro crash. I don't need anything in those 3 rows. How can I delete them before my Do Until loop?
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Sub Mytxt()
Dim Mytxt As String
Mytxt = Application.GetOpenFilename(FileFilter:="EXCEL files (*.txt),*.txt", Title:="Open the Report file you need")

If Mytxt = "" Then Exit Sub
Workbooks.Open Filename:=Mytxt
Open Mytxt For Input As #1
i = 1
Do Until (EOF(1) = True)
Line Input #1, tempstr
Cells(i, 1) = Mid(tempstr, 23, 5)
Cells(i, 2) = Mid(tempstr, 25, 1)
Cells(i, 3) = Mid(tempstr, 33, 3)
i = i + 1
Loop
Close 1
End Sub